This invention relates to a packaging material suitable for packaging photographic photosensitive materials.
For materials that lose their value by exposing them to light, such as photographic photosensitive materials, packaging materials capable of shielding completely from light are used. The packaging materials are necessary to have sealability, moistureproofness and gas barrier properties, without the occurrence of pinholes, in addition to the light-shielding ability. Moreover, it is necessary to have sufficient physical strength and antistatic property to prevent spark discharge and the like. Good bag-making ability, inexpensiveness and excellent appearance are also required. It is difficult to satisfy these properties by using a single film material, and a conventional packaging material is a laminated film shown in FIG. 7 composed of a polyester layer 12, an adhesive layer 13, an aluminum layer 14 and a polyolefin resin layer 15a containing a light-shielding material and a nonionic antistatic agent (Japanese Patent KOKOKU No. 63-26697). The applicant disclosed a packaging material comprising a laminate composed of a paper support and a thermoplastic resin layer formed of a blended resin of high density polyethylene resin and low density polyethylene resin laminated onto at least one side of the paper support (Japanese Patent KOKAI No. 60-35728). Furthermore, the applicant disclosed a packaging material of a laminated film comprising a coextruded double layer film consisting of a linear low density polyethylene resin film layer 16a containing a light-shielding material having a mean particle size of less than 200 m.mu. and a high density polyethylene resin film layer 17a, as shown in FIG. 8 (Japanese Patent KOKAI No. 63-85539).
The packaging material disclosed in Japanese Patent KOKOKU No. 63-26697 is inferior not only in resistance to the occurrence of pinholes but also in physical strength and heat sealing properties. As a result, bag rupture and light leakage trouble frequently occurred. Although the packaging material disclosed in Japanese Patent KOKAI No. 60-35728 is excellent in antistatic property and light shielding ability, it is inferior in resistance to the occurrence of pinholes, moistureproofness, gas barrier, physical strength and heat sealing properties. The packaging material disclosed in Japanese Patent KOKAI No. 63-85539 is excellent in antistatic property, but it is inferior in physical strength and oxygen barrier. Therefore, bag rupture was liable to occur during transportation. It is also inferior in heat sealing properties, and heat seal strength is gradually lowered.